To make New Relic available globally for all your projects within Drupal VM, make the following changes inside config.yml, then run vagrant up (or vagrant provision if the VM is already built):

# Make sure newrelic is not commented out in the list of installed_extras:
installed_extras:
[...]
- newrelic
[...]
# Set vars for your New Relic account:
# `newrelic` must be in installed_extras for this to work.
newrelic_license_key: yourkey
# Customize any additional vars relevant to your project needs.
# See all vars: https://github.com/weareinteractive/ansible-newrelic#variables